Modulated-carrier wave-signal receiver



`IVIaucPnl 31, V1942. R. FREEMAN MODULATED-CRRIER WAVE-SIGNAL RECEIVER Patented Mar. 31, 1942 MGDULATED-CARRIER WAVE-SIGNAL RECEIVER Robert Lee Freeman, Flushing, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application August 15, 1940, Serial No. 352,757

(Cl. Z50-20) 8 Claims.

This invention relates to a signal-translating channel for translating, with a predetermined amplitude distortion, a signal input including signal components within a predetermined frequency range and, while the invention is of general utility, it is particularly useful for effecting a gamma adjustment of a translated television signal.

There are many uses in signaling systems for a signal-translating channel which is effective to translate, with a predetermined amplitude distortion, a signal input including signal components within a predetermined frequency range. Thus, such a network may be used to effect a gamma adjustment of a translated video signal in a television system. In photography, a lm is said to have a gamma which deviates from unity in accordance with differences in relative detail or contrast for the brighter or darker portions of the image represented thereby, compared to other portions thereof, with resp-ect to the corresponding contrasts of the original scene, that is, a nonlinear incremental transfer ratio over the amplitude range of the image. This same concept is useful in television. Briefly, the gamma of any television reproduction may be defined as the slope of the stimulus-response curve plotted on a logarithmic scale. Obviously, only where gamma is unity is there a linear relationship between the stimulus and the response over the entire response range of the system.

Another well-known example of an installation in which it may be desirable tov produce a predetermined amplitude distortion is an installation comprising a voltage or power amplifier, the translating characteristic of which is desired to be linear but which varies from linearity due to the curvature of the transfer characteristics of the vacuum tubes utilized in the amplifier. In such a case, it is desirable to provide in cascade therewith a distorting signal-translating channel for effecting a distortion which is complementary to that effected by the amplifier.

Furthermore, in modulators usedin transmitters and, particularly, in the case of grid-modulated power ampliflers utilized in television transmitters, considerable radio-frequency driving power is needed to provide-a linear` modulation characteristic near full modulation. Thus, by the use of a signal-translating channel for effecting a compensatory amplitude distortion, considerably less driving power for such a modulator can be utilized with satisfactory results.

It is an object of the invention, therefore,

to provide an improved signal-translating channel for translating with a predetermined amplitude distortion a signal input including components within a predetermined frequency range.

It is a further object of the invention to provide an improved signal-translating channel for translating with a predetermined distortion which is adjustable by the user a signal input including frequency components within a predetermined frequency range.

It is still another object of the invention to provide a signal-translating channel which comprises a passive network, that is, one containing no internal sources of power, for translating with a predetermined amplitude distortion a signal input including components within a predetermined frequency range.

In accordance with the invention, a modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range comprises a source of oscillations having a frequency which is high with respect to any of the modulation-frequencies within the predetermined range, together with means for frequency-modulating the oscillations with the modulation-signal components to derive a frequency-modulated signal. A signal-translating circuit having a nonlinear frequency-transmission characteristic is provided for translating the frequency-modulated signal, and means are provided for amplitude-detecting the translated frequency-modulated signal to derive the desired distorted output signal.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawing is a circuit diagram, partly schematic, of a complete television receiver of the superheterodyne type embodying an arrangement, in accordance with the invention, in the video-frequency channel thereof for effecting a gamma control; Fig. 2 is a circuit diagram of a specific modification of a portionof the gammacontrolling arrangement of Fig. 1; Figs. 3 and 4 comprise graphs utilized to explain the operation of the circuit of Fig. 2 in the receiver of Fig. 1; Fig. 5 is a circuit diagram of` a portion of the circuit of Fig. 1 arranged in accordance with the present invention; while Figs. 6 and 7 are circuit diagrams of different modifications of a portion of the system of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, the system there represented comprises a receiver of the superheterodyne type including an antenna system I0, I| connected to a radio-frequency amplifier I2 to which are connected in cascade, in the order named, an oscillator-modulator I3, an intermediate-frequency amplifier Ill, a detector I5, a gamma-controlling arrangement il, a video-frequency amplifier I8, and an image-reproducing device I9. A linescanning generator 2i] and a field-scanning generator 2| are coupled to an output circuit of detector I through a synchronizing-signal separator 22, the generators and 2| being coupled to the deiiecting means of the image-reproducing device I9 to provide suitable'scanning elds. An audio-signal translating channel 23 and sound reproducer 2li are coupled to an output circuit of intermediate-frequency amplifier I4 in order to reproduce the sound signals accompanying the received television program. The stages or units I5-E5, inclusive, and Iii-2t, inclusive, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein.

Referring brieiiy, however, to the operation of the system described above, television signals intercepted by antenna circuit I0, II are selected and amplied in radio-frequency amplier I2 and coupled to the oscillator-modulator I3 wherein they are converted into intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier I4 and delivered to the detector I5. The modulation components of the signal are derived by the detector I5 and are supplied to the video-frequency amplifier I8 through the unit II. The amplied video-frequency signals are thereafter applied, in the usual manner, to a brilliancy-control electrode of the image-reproducing device I9. The intensity of the scanning ray of device I9 is thus modulated or controlled in accordance with the video-frequency voltages impressed upon the control electrode in the usual manner. Scanning waves are generated in the line-scanning and field-scanning generators 2D and 2|, which are controlled by synchronizing-voltage pulses supplied from detector I5 through synchronizing-signal separator 22, and applied to the scanning elements of the image-reproducing device I9 to produce electric scanning fields, thereby to deflect the scanning ray in two directions normal to each other so as to trace a rectilinear scanning pattern on the screen and thereby to reconstruct the transmitted image. Sound signals accompanying the television programs are translated by unit 23 and reproduced in loudspeaker 24 in a conventional manner.

Coming now to the portion of the system of Fig. 1 embodying the present invention, the unit II comprises a signal-translating channel in a modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range; specifically, the unit I1 is utilized for translating the video-signal output from detector I5, which includes signal components within a predetermined frequency range, to the video-frequency amplifier I8 with a predetermined amplitude distortion. The unit I1 comprises three subunits coupled in cascade, the sub-units including a frequency modulator and high-frequency oscillator 3D, a nonlinear translating circuit 3|, and a linear detector 32.- The unit comprises a source of oscillations having a frequency which is high with respect to any of the modulation frequencies o1' frequencies Within the video-frequency range of the signal being translated, together with means for frequency-modulating the oscillations with the video-signal modulationsignal components or the output from detector I5 to derive a frequency-modulated signal. The frequency-modulated signal is translated through the signal-translating circuit 3| having a nonlinear frequency-transmission characteristic and is thereafter detected in the linear detector 32 in order to provide the desired distorted input signal for video-frequency amplifier I8.

In Fig. 2 there is illustrated a circuit which may be utilized as the nonlinear signal-translating circuit 3| of Fig. 1. The unit 3| may be sub.

stituted in the circuit of Fig. 1 by interconnecting correspondingly marked terminals. The unit of Fig. 2 comprises a parallel-resonant circuit including an adjustable condenser 33 in parallel with which is coupled a series-connected inductance 34 and resistor 35.

Reference is made to the graphs of Figs. 3 and 4 for an explanation of the operating characteristics of the circuit of Fig. 2 when it is included as the nonlinear translating circuit of Fig. l. In Fig. 3 there is illustrated the relative-frequencyresponse characteristic of the resonant circuit 33, 34, 35 of Fig. 2. In considering the graph of Fig. 3, reference is made to three portions of the relative frequency-response characteristic of different average response, designated as I, II, and III, each of which is assumed to include a frequency range at least as great as the video-frequency range of the television signal being translated. In order to operate in a selected range, the relative frequency between the frequency of the oscillator of unit 30 and the resonant frequency of tuned circuit 33, 34, 35 is properly adjusted. This may be done either by varying the frequency of the oscillations or the tuning of the resonant circuit. Thus, it is seen that the frequency-response characteristic in the operating range I is concave upward and that a predetermined corresponding distortion of the translated frequency-modulated signal is effected when the frequency-modulated signal output of unit 30 is translated on this portion of the characteristic. Furthermore, it is seen that the response characteristic over the portion II is more nearly linear and that less distortion is effected by operation Within this portion of the characteristic. However, in the range III the frequency-response characteristic is concave downward so that a different type of distortion is effected by operation within this portion of the characteristic.

For an explanation of the eiect of translating the frequency-modulated signal through a circuit having a nonlinear frequency-response characteristic, speciiic reference is made to the graphs of Fig. 4 wherein a portion of a frequency-response characteristic X, Y corresponding to the characteristic within portion I of Fig. 3 is illustrated. If it is assumed that the frequency-modulated signal translated is of constant amplitude and has a sinusoidal frequency variation with time, representing a sinusoidal modulation component, as illustrated by curve a of Fig. 4, a frequency-modulated voltage amplitude modulated in accordance with curve b is developed across the output terminals E, F of the unit 3|, and it is thus seen that a predetermined amplitude distortion of the frequency-modulated signal is effectedA by translation through the unit 3|. Correspondingly, different types of distortion are ef' fected by translation of the signal Within the porl tions II and III.

The type of characteristic with which the signals are effectively translated through the nonlinear translating circuit 3| can, as stated above, be selected by means of an adjustment of condenser 33 which varies the mean resonant frequency of the tuned circuit 33, 34, 35 and thus effectively displaces the portions I, II, and III on the frequency scale of Fig. 3. Alternatively, as also stated above, the mean frequency of the oscillator comprised in unit 3|] can be adjusted to vary the effective operating characteristic of unit 3| as such adjustment electively displaces the portions I, II, III on the frequency scale of Fig. 3.

From Fig. 3 it will be noted that the average amplitude of the signal output of unit 3| varies in accordance with the portion of the characteristic selected for operation. Therefore, it may be desirable simultaneously to adjust the average amplitude of the received signal to compensate for this effect. Therefore, the unicontrol member U of Fig. 2 is provided for simultaneously adjusting the value of condenser 33 and the signal setting of the volume control or the gain characteristic at any suitable point in the receiver.

In Fig. there is shown a detailed circuit diagram of the portions of the system of Fig. 1 constituting the present invention. Circuit elements which are similar to those of the preceding iigures have identical reference numerals. It will be understood that the circuit of Fig. 5 can be connected into the circuit of Fig. 1 by connecting terminals of the circuit of Fig. 5 to correspondingly marked terminals of Fig. 1.

The unit 36 of Fig. 5 comprises a vacuum tube 36 connected to function as a well-known type of variable reactance tube. The tube is provided with a grid-leak resistor 37, a cathode-biasing resistor 38 shunted by a condenser 39, and a condenser 40 connected between the anode and control electrode of the tube. There is also included in unit 36 of Fig. 5 an oscillator including a tube 4| having a frequency-determining circuit comprising an inductance ,42 and a variable condenser 43 coupled to the input electrodes of the tube through a coupling condenser 44 and grid leak 45. A suitable feed-back circuit is provided including an inductance 46 inductively coupled to inductance 42 and connected to the second grid of tube 4|. The anode circuit of reactance tube 36 is coupled across frequency-determining circuit 42, 43.

The unit 3| of Fig. 5 is identical with the circuit of Fig. 2 While the unit 32 thereof comprises a diode detector 50, having a load circuit including a resistor 5|, from which the detected video signals are coupled through a suitable filter circuit including a series resistor 55 and a shunt condenser 54 to the output terminals G, H. The unit 32 thus comprises a linear amplitude-modulation detector.

In considering the operation of the circuit of Fig. 5 in the receiver of Fig. l, it will be seen that tube 4| is comprised in an oscillator circuit of conventional type and that the tube 36 functions as a well-known type of reactance control tube instantaneously to control the frequency of the oscillator in accordance with thevideo-frequency signal input to terminals A, B. In the absence of a signal input to terminals A, B, the circuit is so adjusted that the voltage eg developed across the voltage across the frequency-determining circuit 42, 43 by 90 degrees. The alternating current component of the anode circuit of tube 36 due to this input voltage also leads the voltage across the frequency-determining circuit of the oscillator by degrees. Therefore, the reactance tube 36 with no signal input applied thereto simulates a capacitance in shunt with the frequencydetermining circuit of the oscillator having a value C=gmC4oR37 where,

v C4o=capacitance of condenser 40,' R37=resistance of resistor 31; and gm :transconductance of tube 36.

When a video signal es which is to be distorted is applied to the input electrodes of the reactance tube 36, it causes the transconductance of the tube to Vary. As the signal increases in a positive direction, the frequency of the oscillator is decreased and Vice-versa. The anode current of the tube 4|, therefore, constitutes a frequencymodulated signal of constant amplitude which is translated through the nonlinear translating circuit 3| and thus develops a frequency-modulated voltage at the output terminals E, F which is also amplitude-modulated. The amplitude-modulation envelope of this voltage is that of the original input signal es distorted in a predetermined manner dependent upon the portion of the frequencyresponse characteristic of unit 3| over which the signal is translated. 'Ihe signal output of the linear amplitude detector 32 thus corresponds to the Video-signal input to unit 3| distorted in a predetermined manner dependent upon the portion of the frequency-response characteristic of unit 3| which is utilized.

In Fig. 6 there is illustrated a unit 3|'. which may be substituted for the unit 3| in the preceding arrangements by connecting correspondingly marked terminals of the unit 3| to those of the circuit of Fig. 1. The unit 3| comprises two similar filter networks coupled in cascade by means of a screen-grid tube 56. Each of these lter networks effectively comprises a low-pass filter whole-section including a series arm Ls and mid-shunt arms C, together with a terminating m-derived filter section having a shunt arm MC and a series arm including parallel-connected inductance L and capacitance C in series with a terminating resistor R. In order to provide a diierentiating type of lter network, there are coupled across the input terminals of each lter section a condenser C and an inductance LS having a value equal to the value of series inductor Ls of the filter. Each of the low-pass filter networks utilized in unit 3|' is described in detail in the copending application of Harold A. Wheeler, Serial No. 313,360, led January 11, 1940, Patent No. 2,247,538 issued July 1, 1941, and assigned to the same assignee as the present application, the filter networks of unit 3|' being identical to that illustrated in Fig. 1b of the copending application. Each of the lter networks thusv comprises an arrangement in which the transmission ratio is directly proportional to the frequency of the applied signal. Therefore, the over-all characteristic of unit 3| of Fig. 6 is such that the transmission ratio varies as the square of the signal input supplied thereto and the unit 3|' can be used in the receiver of Fig. 1 to effect a gamma, correction of two.

In Fig. 7 there is shown a simplified arrangeresistor 3`| in the input circuit of tube 36 leadsl ment having a characteristic similar to that of Fig. 6, that is, in which the transmission ratio varies as the square of the applied signal. The circuit of Fig. 7 comprises a lter network eX- actly like either one of the two filter networks utilized in the circuit of Fig. 6 except that adjacent capacitance elements have been combined to form elements C and C and the remaining circuit elements thereof have identical reference characters. However, in the circuit of Fig. '7, the output voltage supplied to terminals C, D is taken from the series inductor Ls of the iilter. A filter network in accordance with that illustrated in Fig. 7, as brought out above, has a transmission characteristic which varies linearly with frequency if the output voltage is taken from the terminating resistor R of the filter. However, in such a lter network the current through the series arm Ls is directly proportional to the voltage across the shunt element Ls. Since the voltage across the shunt element Ls is directly proportional to frequency, the series current is thus likewise proportional to frequency. Therefore, the voltage drop produced across the series arm Ls is proportional to the square of the frequency and the network of Fig. 7 thus has a transmission ratio which varies as the square of the frequency.

Various combinations of the circuits of Fig. 6 and Fig. l can be utilized in cascade to obtain various desired output characteristics. That is, the use of two such square-law networks as illustrated in Fig. 6 or Fig. 7 will provide an over-all transmission ratio which is proportional to the fourth power of the frequency of the input signal, or the use of one of the square-law filter networks together with a linear filter network will provide an arrangement having an over-all transmission ratio proportional to the third power of the frequency of the translated signal. rFherefore, combinations of the lter networks coupled in cascade may be utilized in the circuit of Fig. 1 and the signal input for the linear detector 32 can be derived from various possible output tel'- minations along the chain of such filters to provide an over-all gamma of 2, 3, 4, etc.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude di"- tortion a signal input including signal components within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-inodulating said oscillations with said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit having a nonlinear frequency-transrnissicn ci tic for translating said frequency-modulated signal, and means for detecting said translated frequency-modulated signal to derive the desired distorted output signal.

2. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect t0 any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations with said modulation-signal components to derive a frequency-modulated signal, a signal-translating circuit having a nonlinear frequency-transmission characteristic for translating said frequency-modulated signal, and means comprising a linear amplitude-modulation detector for detecting said translated frequencymodulated signal t0 derive the desired distorted output signal.

3. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations with said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit having a frequency-transmission characteristic including a plurality of different nonlinear portions for translating said frequency-modulated signal, means for adjusting said circuit for operation on any predetermined one of said portions, and means for detecting said translated frequencymodulated signal to derive the desired distorted output signal.

4. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations with said modulation-signal components to derive a frequency-modulated signal, a signal-translating circuit having a frequency-transmission characteristic including a plurality of different nonlinear portions for translating said frequency-modulated signal, means including means for varying the mean frequency of said source of oscillations for adjusting said circuit for operation on any selected one of said portions, and means for detecting said translated frequency-modulated signal to derive the desired distorted output signal.

5. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations with said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit comprising a parallel-resonant circuit having a frequency-transmission characteristic including different nonlinear portions for translating said frequency-modulated signal, means including means for varying the resonant frequency of said circuit for adjusting said circuit for operation on any selected one of said portions, and means for detecting said translated frequency-modulated signal to derive the desired distorted output signal.

6. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components Within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations with said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit comprising a parallel-resonant circuit having a frequency-transmission characteristic including different nonlinear portions of different average response for translating said frequency-modulated signal, means including means for varying the resonant frequency of said circuit for adjusting said circuit for operation on any selected one of said portions and for simultaneously compensating for the effect of said diierent responses, and means for detecting said translated frequencymodulated signal to derive the desired distorted output signal.

7. A modulated-carrier Wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal compo. nents Within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations With said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit including a differentiating lter circuit having a nonlinear frequency-transmission characteristic for translating said frequency-modulated signal, and means for detecting said translated frequencymodulated signal to derive the desired distorted output signal.

8. A modulated-carrier wave-signal receiver for translating with a predetermined amplitude distortion a signal input including signal components Within a predetermined modulation-frequency range comprising, a source of oscillations having a frequency which is high with respect to any ,of the modulation frequencies within said predetermined range, means for frequency-modulating said oscillations With said modulationsignal components to derive a frequency-modulated signal, a signal-translating circuit having a square-law frequency-transmission characteristic for translating said frequency-modulated signal, and means for detecting said translated frequency-modulated signal to derive the desired distorted output signal.

' ROBERT LEE FREEMAN. 

